One function of an information technology (IT) department in a company is to manage the company's internet protocol (IP) addresses. It is not unusual for companies to manage thousands or even tens of thousands of IP addresses. To help manage IP addresses, companies often use subnets to make the process more manageable. Subnets are comprised of blocks of IP addresses.
Subnets are commonly identified by writing the starting IF address followed by a slash followed by the bit length of the subnet. For example, subnet 10.0.0.0/24 denotes a subnet with 256 IP addresses ranging from 10.0.0.0 to 10.0.0.255. Subnet 10.0.0.0/25 denotes a subnet with 128 IP addresses ranging from 10.0.0.0 to 10.0.0.127. It is common for IT departments to assign subnets of different sizes to internal departments and/or external customers, e.g., depending on function or group. FIG. 1, which includes generic nomenclature so as not to be limited to a specific numbering system, is a schematic diagram of a subnet register and includes nested subnets. The bottom level includes the IP addresses and any number of levels may be placed above depending on the particular application.
When you choose a subnet to assign, the subnet you choose will have a big impact on future subnets choices. If you choose a subnet that is much bigger than you need, then many other possible subnets are in effect wasted. If you choose a subnet that is near another subnet but not directly adjacent, the available subnets in between may be too small to be used and are effectively wasted. Existing technology often assigns the next available subnet regardless of future needs.